To prevent water colors from crawling, add a few drops of ammonia or lime water, or a solution of sal soda.

** Small Electrical Hydrogen Generator [54]

A small hydrogen generator may be made from a fruit jar, A (see sketch), with two tubes, B and C, soldered in the top.  The plates E can be made of tin or galvanized iron, and should be separated about 1/8 in. by small pieces of wood.  One of these plates is connected to metal top, and the wire from the other passes through the tube B, which is filled with melted rosin or wax, to make it airtight.  This wire connects to one side of a battery of two cells, the other wire being soldered to the metal top of the jar, as shown.  The jar is partly filled with a very dilute solution of sulphuric acid, about 1 part of acid to 20 of water.

When the current of electricity passes between the plates E, hydrogen gas is generated, which rises and passes through the rubber hose D, into the receiver G. This is a wide-mouth bottle, which is filled with water and inverted over a pan of water, F.

[Illustration:  Hydrogen Generator]

The gas bubbling up displaces the water and fills the bottle.

If the receiver is removed when half full of gas, the remaining space will be filled with air, which will mix with the gas and form an explosive mixture.  If a lighted match is then held near the mouth of the bottle a sharp report will be heard.

If the bottle is fitted with a cork containing two wires nearly touching, and the apparatus connected with an induction coil, in such a manner that a spark will be produced inside the bottle, the explosion will blowout the cork or possibly break the bottle.  Caution should be used to avoid being struck by pieces of flying glass if this experiment is tried, and under no condition should a lighted match or spark be brought near the end of the rubber hose D, as the presence of a little air in the generator will make an explosive mixture which would probably break the jar.

** Gasoline Burner for Model Work [55]

When making a small model traction engine or a locomotive the question arises, “What shall the fuel be?” If you have decided to use gasoline, then a suitable burner is necessary.  A piece of brass tubing about 3 in. in diameter and 6 in. long with caps screwed on both ends and fitted with a filling plug and a bicycle valve makes a good gasoline supply tank, says the Model Engineer, London.  The bicycle valve is used to give the tank an air pressure which forces the gasoline to the burner.

The burner is made from a piece of brass tube, A, as is shown in the illustration, 1/2 in. in diameter and 2-1/2 in. long, which is plugged up at both ends, one end being drilled and reamed out to 5/16 in.  Three rows of holes 1/16 in. in diameter are drilled in the brass tube.  One row is drilled to come directly on top, and the other two at about 45 degrees from the vertical.  It is then fitted to a sheet steel base, B, by means of the clips, C C, Fig. 1.  A piece of 1/8-in. copper pipe, P, is then coiled around the brass tube, A, which forms the vaporizing coil.  This coil should have a diameter